Flat panel displays are fabricated using many techniques. See, for example, Liquid Crystal Flat Panel Displays by William C. O'Mara (Chapman & Hall, New York 1993), and other similar publications. These displays use transparent glass plates as substrates, and electrical traces are sputtered in a pattern of parallel lines that form a first set of conductive traces. A transparent conductor such as Indium Tin Oxide (ITO) is sputtered over the traces to disperse an electrical charge across transparent areas not blocked by the traces. Alternatively, the traces can be formed entirely of ITO. A second substrate is similarly coated with a set of traces having a transparent conductive layer.
Layers are applied over the substrates and patterned to orient liquid crystals in twisted nematic (TN) or super-twisted-nematic (STN) configurations. The two substrates are spaced apart and the space between the two substrates is filled with a liquid crystal material. Solder interconnects or wire bonds are connect the traces to external an external drive. Pairs of conductors from either set are selected and energized to alter the optical transmission properties of the liquid crystal material.
In another embodiment, the traces do not define an orthogonal grid, but are organized to form alpha-numeric displays or graphic images. In a further embodiment, an active display on a transparent substrate is sputtered or printed and uses memory elements to continuously drive a each display element depending on information written to the memory element. In another embodiment, disclosed in SID DIGEST 90, article 12.6, the liquid crystal material can be polymerically dispersed to form a Liquid Crystal Polymer Matrix (LCPC). LCPCs are typically disposed in ultra-violet polymerized acrylic polymers. The liquid crystals are homogenized into the polymer, and the emulsion is coated onto a substrate. Ultra violet light is applied to the emulsion. The emulsion hardens, and bubbles of liquid crystal material are held in a rigid polymeric matrix.
Reflective liquid crystal polymer matrix displays are disclosed in U.S. Pat. No. 4,435,047. A first sheet has a transparent Indium-Tin-Oxide (ITO)conductive areas and a second sheet has electrically conductive inks formed into display areas. The sheets can be glass, but in practice have been formed of Mylar polyester. A dispersion of liquid crystal material in a binder is coated on the first sheet, and the second sheet is pressed onto the liquid crystal material. Electrical charges applied to opposing conductive areas operate on the liquid crystal material to expose display areas. Taliq Corporation of Sunnyvale, California currently produces products which form electrical interconnection by offsetting the two sheets and contacting trace conductors from each of the two sheets.
Image displays can provide color images if a color filter array is formed over the pixels of the display. In U.S. Pat. No. 5,462,833, three color layers are formed on a transparent substrate. In this patent, a transparent electrode layer is formed over the color filter. The filter plate is aligned onto a liquid crystal layer. The plate is glass and has silver halide, color-forming layers. A transparent electrode material is sputtered at high temperature over the CFA. In practice, the presence of the transparent electrode material causes ionic migration of the dyes in the dye layers.
Multiple, separate layers on multiple plates are presently used to build up the display. The electrical traces and transparent conductive layers are typically formed through repeated vacuum deposition of materials on the substrate. These processes are expensive and require long processing times on capital intensive equipment. Because most display structures are formed of glass, two sheets are used and are offset to permit connection to two separate and exposed sets of traces that are disposed on separate sheets.